The role of nanotechnology in industrial water treatment

Engineering Irrigation Drippers with Rechargeable N-Halamine Nanoparticles for Antifouling Applications

The increased demand for water highlights the need to utilize reclaimed water of various types. In agriculture, for example, which is considered the largest consumer of freshwater, irrigation with treated wastewater can replace much of the need for freshwater. Wastewater is generally used for irrigation through drippers, releasing small amounts of water to the crops. The contaminants found in treated wastewater increase the accumulation of fouling on the drippers, ultimately culminating in blocking of water exit. Thus, there is a crucial need to develop novel approaches to limit biofilm formation on the dripper. Here, we describe the synthesis of N-halamine-derivatized cross-linked polymethacrylamide nanoparticles (NPs) by copolymerization of the monomer methacrylamide and the cross-linker monomer N, N-methylenebisacrylamide and their subsequent embedding in the polyethylene that is used to fabricate the drippers. The newly designed drip system was activated by chlorinating the incorporated NPs and then was fully characterized. The nanofunctionalized drippers were tested in the field, showing excellent antifouling activity for at least 5 months compared to the control. In addition, the inherent recharging capacity of the antifouling NPs constitutes yet another valuable advantage of the currently reported technology.

Silver Nanowire-Modified Filter with Controllable Silver Ion Release for Point-of-Use Disinfection

Waterborne diseases related to unsafe water are still major threats to public health in some developing countries and rural areas. Providing affordable and safe drinking water globally remains a great challenge in the coming decades. In this study, we develop a high-throughput and conductive silver nanowire (AgNW)-modified composite filter via depositing thin and ultralong AgNWs on a macroporous substrate. An electrochemical filtration cell (EFC) equipped with the composite filter achieves controllable Ag⁺ release at a μg L^-1 level and superior bacterial inactivation performance (>6-log inactivation efficiency) with an operation voltage of only 1 V at a high flux of 100 m³ h^-1 m^-2. Under such operation conditions, each composite filter (effective area: 0.79 cm²) can treat at least 750 mL of the bacterial suspension (∼10⁷ CFU mL^-1 of Escherichia coli) with a low effluent Ag⁺ concentration below 50 μg L^-1 and almost negligible energy consumption of only ∼70 J m^-3.

A water lily-inspired hierarchical design for stable and efficient solar evaporation of high-salinity brine

In recent years, interfacial solar vapor generation has shown great potential in realizing desalination and wastewater treatment with high energy conversion efficiency. However, high evaporation rate cannot be maintained because of the seemingly unavoidable fouling or salt accumulation on the solar absorbers. The degradation accelerates as the solute concentration increases. Here, we demonstrate a water lily-inspired hierarchical structure that enables efficient evaporation (~80% solar-to-vapor efficiency) out of high-salinity brine [10 weight % (wt %)] and wastewater containing heavy metal ions (30 wt %). More notably, neither decrease in evaporation rate nor fouling on absorbers was observed during the entire evaporation process until water and solute were completely separated. With the capabilities of stable and high-rate evaporation out of high-salinity brine and the effective separation of solute from water, it is expected that this technology can have direct implications in various fields such as wastewater treatment, sea-salt production, and metal recycling.

Electroactive Membranes for Water Treatment: Enhanced Treatment Functionalities, Energy Considerations, and Future Challenges

To meet the increasing demand for water, potable water providers are turning toward unconventional waters, such as seawater and wastewater. These highly saline and/or heavily contaminated water sources are difficult to treat, demanding the use of advanced technology not typically used to treat conventional water sources such as river water or fresh groundwater. Of these advanced technologies, membrane separation processes are fast becoming the most widely used methods to convert these marginal waters into useful resources. The main factors contributing to the widespread adoption of membrane separation processes for water treatment include their modular nature, small physical footprint, and relative energy efficiency compared to traditional distillation processes. In addition, membranes present a physical barrier to pathogens, which is an attractive feature in terms of disinfection credits. However, traditional membrane materials suffer from several distinct drawbacks, which include membrane fouling (the accumulation of material on the membrane surface that blocks the flow of water), the need for high-pressure membranes (such as reverse osmosis (RO) or nanofiltration (NF)) or membrane/thermal processes (e.g., membrane distillation (MD)) to remove small contaminant compounds (e.g., trace metals, salt, endocrine disrupting compounds), and a pressure-driven membrane's inability to effectively remove small, uncharged molecules (e.g., N-nitrosodimethylamine (NDMA), phenol, acetone, and boron). Electrically driven physical and chemical phenomena, such as electrophoresis, electrostatic repulsion, dielectrophoresis, and electricity-driven redox reactions, have long been coupled to membrane-based separation processes, in a process known as electrofiltration. However, it is only in recent years that appropriate membrane materials (i.e., electrically conducting membranes (EMs)) have been developed that enable the efficient use of these electro-driven processes. Specifically, the development of EM materials (both polymeric and inorganic) have reduced the energy consumption of electrofiltration by using the membrane as an electrode in an electrochemical circuit. In essence, a membrane-electrode allows for the concentrated delivery of electrical energy directly to the membrane/water interface where the actual separation process takes place. In the past, metal electrodes were placed on either side of the membrane, which resulted in large potentials needed to drive electrochemical/electrokinetic phenomena. The use of a membrane-electrode dramatically reduces the required potentials, which reduces energy consumption and can also eliminate electrocorrosion and the formation of undesirable byproducts. In this Account, we review recent developments in the field of electrofiltration, with a focus on two water treatment applications: desalination and water reuse (wastewater or contaminated groundwater recycling). Specifically, we discuss how EMs can be used to minimize multiple forms of fouling (biofouling, mineral scaling, organic fouling); how electrochemical reactions at the membrane/water interface are used to destroy toxic contaminants, clean a membrane surface, and transform the local pH environment, which enhances the rejection of certain contaminants; how electric fields and electrostatic forces can be used to reorient molecules at the membrane/water interface; and how electrical energy can be transformed into thermal energy to drive separation processes. A special emphasis is placed on explicitly defining the additional energy consumption associated with the electrochemical phenomena, as well as the additional cost associated with fabricating EM materials. In addition, we will discuss current limitations of the electrofiltration process, with particular attention given to the current limitations of membrane materials and the future research needs in the area of membrane materials and module development.